This invention relates generally to field emission displays and, more particularly, to a conductive, light-absorbing praseodymium-manganese oxide layer deposited on the surface of a baseplate within a field emission display to bleed off surface charge and absorb stray electrons.
Many devices such as computers and televisions require the use of a display. Typically, the cathode ray tube (CRT) has been used to perform this function. The CRT consists of a scanning electron gun directed toward a phosphor-coated screen. The electron gun emits a stream of electrons that impinge upon individual phosphor picture elements or pixels on the screen. When the electrons strike the pixels, they cause the energy level of the phosphor to increase. As the energy level declines from this excited state, the pixels emit photons. These photons pass through the screen to be seen by a viewer as a point of light. The CRT, however, has a number of disadvantages. In order to scan the entire width of the screen, the CRT screen must be relatvely distant from the electron gun. This makes the entire unit large and bulky. The CRT also requires a significant amount of power to operate.
More modem devices such as laptop computers require a light weight, portable screen. Currently, such screens use electroluminescent or liquid crystal display technology. A promising technology to replace these screens is the field emission display. The field emission display (FED) utilizes a baseplate of cold cathode emitter tips as a source of electrons in place of the scanning electron gun used in the CRT. When placed in an electric field, these emitter tips emit a stream of electrons in the direction of a faceplate to which phosphor pixels are adhered. Instead of a single gun firing electrons at the pixels, the FED has an array of emitter tips. Each of the emitter tips are individually addressable, and one or more of the emitter tips correspond to a single phosphor pixel on the faceplate.
One of the problems associated with an FED is that not all of the photons that are released from the pixels pass through the faceplate to be seen by the viewer as points of light. Rather, nearly half of the photons will proceed in the general direction of the baseplate, and may impinge upon the emitter tips and/or circuitry within the FED. This may cause an undesirable photoelectric effect, and any reflected light from the baseplate reduces the contrast of the FED. A further problem is that not all of the electrons released by the emitter tips actually excite their targeted pixel. Instead, some of these electrons are reflected internally, and may excite a non-targeted pixel.
Accordingly, there is a need in the art for a field emission display which minimizes the photoelectric effect, and the problems associated with internally-reflected electrons. The present invention fulfills these needs, and provides other related advantages.
In brief, this invention is generally directed to a conductive, light absorbing praseodymium-manganese oxide layer coated on the interior surface of an FED baseplate. The praseodymium-manganese oxide layer reduces the photoelectric effect and damage associated by reflected electrons from the faceplate, and improves display image and contrast due to absorption of any ambient light reaching the baseplate and/or by absorption of any photons emitted in the direction of the baseplate.
In one embodiment, a conductive and light-absorbing baseplate for use in a field emission display is disclosed. At least a portion of the interior surface of the baseplate (i.e., the surface opposite the faceplate) is coated with a praseodymium-manganese oxide layer having a resistivity which does not exceed 1xc3x97105 xcexa9xc2x7cm, preferably does not exceed 1xc3x97104 xcexa9xc2x7cm, and more preferably does not exceed 1xc3x97103 xcexa9xc2x7cm. The praseodymnium-manganese oxide layer is coated on the baseplate at a thickness ranging from 1,000 xc3x85 to 15,000 xc3x85, and has a light absorption coefficient of at least 1xc3x97105 cmxe2x88x921 at a wavelength of 500 nm.
In a related embodiment, an FED is disclosed which contains the conductive and light-absorbing baseplate of this invention. Such displays are particularly suited for use in products which are employed under high ambient light conditions, including (but not limited to) the screen of a laptop computer.
In a further embodiment, a process for manufacturing a conductive and light-absorbing baseplate is disclosed. The process includes coating the interior surface of the baseplate with a layer of praseodymium-manganese oxide having a resistivity which does not exceed 1xc3x97105 xcexa9xc2x7cm. Suitable coating techniques include (but are not limited to) deposition by RF sputtering.
In still a further embodiment, a process for manufacturing a conductive and light-absorbing praseodymium-manganese oxide material is disclosed. This process includes heating a mixture of a praseodymium compound and a manganese compound at a temperature ranging from 1200-1500xc2x0 C. for a period of time sufficient to yield the praseodymium-manganese oxide material. The praseodymium compound is Pr6O11 and the manganese compound is selected from MnO2 and Mn(CO3)2. Furthermore, the ratio of praseodymium to manganese within the peseodymium-manganese oxide material is such that the material has a resistivity (after coating a layer of the same on the baseplate) that does not exceed 1xc3x97105 xcexa9xc2x7cm.
These and other aspects of this invention will become evident upon reference to the attached figures and the following detailed description.